One of the most widely used processes for preparing corrugating medium is the neutral sulfite semichemical process hereinafter referred to as the NSSC process. The cooking liquor in said process utilizes a molar ratio of sodium sulfite to sodium carbonate of from about 7 to 1 to about 3 to 1 which produces a pulping yield of about 65 to 80%. If desired, various buffers can be added such as sodium bicarbonate or sodium hydroxide although the bicarbonate is sometimes preferred since it does not darken the pulp as much as the hydroxide. An improvement on the NSSC process which uses much less sodium sulfite is disclosed in U.S. Pat. No. 3,003,909. A typical process suitable for making corrugated paperboard from hardwoods includes a ratio of sodium sulfite to sodium bicarbonate of 5 to 1, a concentration of liquor of 35 grams per liter, 14% of chemical on the basis of wood, a temperature of 170.degree.C. at a pressure of 100 pounds per square inch for about 2 to 3 hours and a yield of 70%. However, the presence of the sulfur in the cooking liquor is very objectionable ecologically since the end products of the decomposition of liquors from the NSSC process include hydrogen sulfide and sulfur dioxide both of which are malodorous and corrosive thus tending to pollute the atmosphere.